The present invention relates to a clamp device which grips and fixes the inner circumferential surface of a hole in a workpiece, and in particular relates to a clamp device which, while ensuring a support function of supporting an engagement assembly for gripping, also is capable of eliminating at least a portion of the support force after gripping.
Conventionally, clamp devices of various types (so called hole clamps or expansion clamps) that grip the inner circumferential surface of a hole in a workpiece have been put into practical use. For example, a clamp device such as disclosed in Patent Documents #1 and #2 includes a clamp main body, an engagement assembly that passes vertically through a through hole in the clamp main body and that has grip claw portions, a clamp rod for expanding the diameter of the engagement assembly, a drive means consisting of a hydraulic cylinder for driving the clamp rod to and fro, and so on.
The clamp devices described above are hydraulic clamp devices in which the clamp rod for clamping is driven by supply of hydraulic pressure to a hydraulic chamber for clamping of a hydraulic cylinder. A pressurized air type clamp device has also been put into practical use that performs clamp driving with the biasing force of pressurized air, instead of with the hydraulic force. The drive means of such a pressurized air type clamp device comprises a piston member that is linked to the clamp rod, an air operating chamber for clamping above the piston member, an air operating chamber for unclamping below the piston member.
With the clamp devices of Patent Documents #1 and #2, a spring type support mechanism that supports the engagement assembly from below in order to expand the diameter of the engagement assembly comprises an annular support member that supports the lower end of the engagement assembly, a compression spring member that supports the annular support member upwards with elastic force.
And a clamp device has been put into practical use that, instead of the compression spring member, is provided with a hydraulic support mechanism that supports the engagement assembly with hydraulic pressure, or that is provided with a pressurized air type support mechanism that supports the engagement assembly with pneumatic pressure.
Now sometimes it happens that, if the support force of the spring type support mechanism is not sufficient, during clamping, the grip claw portions of the engagement assembly do not properly grip the inner circumferential surface of the hole in the workpiece, but slip with respect to the inner circumferential surface. Due to this it is necessary to employ a spring capable of generating a rather large support force as the compression spring member of the support mechanism. The same is true for a hydraulic support mechanism and for a pressurized air type support mechanism.
It should be understood that a clamp device has also been put into practical use, including a clamping miss detection means that detects whether the clamping is good or bad, by means of blocking a pressurized air ejection hole that is formed in the clamp main body by an annular support member of the support, mechanism that shifts along with the clamp rod, when during clamping the engagement assembly does not properly grip the inner circumferential surface of the hole and slips, and the clamp rod shifts to its limit position in the clamping direction.
On the other hand, since swarf may enter into the interior of the clamp main body when a workpiece clamped with a clamp device of this type is subjected to machining (cutting processing), accordingly, in order to prevent this, an air blowing means is provided to the clamp device and supplies pressurized air to the interior of the clamp main body, so that this air is ejected to the exterior from clearances between the clamp main body, the engagement assembly, the clamp rod, and so on.    Patent Document #1: German Patent No. 4,020,981.    Patent Document #2: Japanese Laid-Open Patent Publication Heisei 11 188551.